The Curonian Lagoon (or Bay, Gulf; Kuršių Marios,Kuršu Joma, Zalew Kuroński, Kurisches Haff, Kуршский залив) is sundered from the Baltic Sea by the Curonian Spit (Kurische Nehrung).
In the 13th century, the area around the lagoon was part of the ancestral lands of the Curonians and old Prussian people. Later it bordered the historical region of Lithuania Minor. At the northern end of the spit, there is a passage to the Baltic Sea, and the place was chosen by the Teutonic Knights in 1252 to found Memelburg castle and the city of Memel. The town is officially called Klaipėda since 1923 when the Memel Territory was separated from the German Empire.
As the new inter-war border, the river that flows into the Curonian Lagoon near Rusnė (German Ruß) was chosen. The river's lower 120km in Germany were called die Memel by Germans, while the upper part located in Lithuania was known as Neman River.
The border also separated the peninsula near the small holiday resort of Nida, Lithuania (German Nidden).
The southern part of spit and lagoon remained in Germany until 1945. This border remains today, as after World War II, the southern end of the split and the German area south of the River, the part of East Prussia with the town Königsberg located in Sambia, became part an exclave of Russia called Kaliningrad Oblast.
